In recent years, it has become evident that transmission lines are suffering a bandwidth shortage as communication speeds become higher. One problem caused by such a bandwidth shortage of transmission lines is intersymbol interference. Intersymbol interference refers to interference between adjacent signals representing a bit value of 0 or 1 while the signals are being transmitted. Intersymbol interference tends to degrade the waveform of the signals to the extent that it is difficult to determine bit values from an input signal applied to a signal reception side.
One solution to the degradation of the waveform of an input signal is waveform equalization. The waveform equalization refers to a technology for intentionally varying part of the waveform of a signal depending on a degradation of the waveform of the signal due to intersymbol interference.
FIG. 1 is a diagram showing an example of an input signal that is degraded due to intersymbol interference.
As shown in FIG. 1, the degradation of the waveform of an input signal includes a precursor component prior to a main tap and a postcursor component subsequent to the main tap.
A decision-feedback equalizer which is capable of removing the effect caused by a postcursor component is disclosed in Non-patent document 1, for example. The decision-feedback equalizer judges a bit value represented by an input signal on the basis of the waveform of the input signal. Based on the determined bit value, the decision-feedback equalizer then removes the effect of the degradation of the waveform of the input signal which has already been received from the next input signal to be applied to the signal reception side.
Therefore, the decision-feedback equalizer can remove the effect caused by a postcursor component from a subsequently applied input signal by taking into consideration postcursor component that has already been determined. However, since a precursor component has not yet been determined, the effect caused by a precursor component cannot be removed from a subsequently applied input signal.
In order to fully eliminate the degradation of a signal due to intersymbol interference, it is necessary to remove the effect caused by a precursor component. To remove the effect caused by a precursor component, it has been customary to use waveform equalization on the signal transmission side which transmits signals. The waveform equalization on the signal transmission side is capable of equalizing waveforms, taking into consideration a precursor, because signals to be transmitted are known in advance.
A technology that is based on a combination of waveform equalization on a signal transmission side and waveform equalization on a signal reception side is disclosed in Non-patent document 2, for example. The technology disclosed in Non-patent document 2 is able to remove both the effect caused by a postcursor component and the effect caused by a precursor component by combining waveform equalization on a signal reception side and decision-feedback equalization on a signal reception side. As a result, the degradation of a signal due to intersymbol interference can completely be eliminated.